Stents are generally known in the medical arts. The term “stent” has been used interchangeably with terms such as “intraluminal vascular graft” and “expansible prosthesis”. As used throughout this specification the term “stent” is intended to have a broad meaning and encompasses any expandable prosthetic device for implantation in a body passageway (e.g., a lumen or artery) to keep a formerly blocked passageway open and/or to provide support to weakened structures (e.g. heart walls, heart valves, venous valves and arteries).
The use of stents has attracted an increasing amount of attention due the potential of these devices to be used, in certain cases, as an alternative to surgery. Generally, a stent is used to obtain and maintain the patency of the body passageway while maintaining the integrity of the passageway. As used in this specification, the term “body passageway” is intended to have a broad meaning and encompasses any duct (e.g., natural or iatrogenic) within the human body and can include a member selected from the group comprising: blood vessels, respiratory ducts, gastrointestinal ducts and the like.
Stent development has evolved to the point where the vast majority of currently available stents rely on controlled plastic deformation of the entire structure of the stent at the target body passageway so that only sufficient force to maintain the patency of the body passageway is applied during expansion of the stent.
Generally, in many of these systems, a stent, in association with a balloon, is delivered to the target area of the body passageway by a catheter system. Once the stent has been properly located (for example, for intravascular implantation the target area of the vessel can be filled with a contrast medium to facilitate visualization during fluoroscopy), the balloon is expanded thereby plastically deforming the entire structure of the stent so that the latter is urged in place against the body passageway. As indicated above, the amount of force applied is at least that necessary to expand the stent (i.e., the applied the force exceeds the minimum force above which the stent material will undergo plastic deformation) while maintaining the patency of the body passageway. At this point, the balloon is deflated and withdrawn within the catheter, and is subsequently removed. Ideally, the stent will remain in place and maintain the target area of the body passageway substantially free of blockage (or narrowing).
See, for example, any of the following patents: U.S. Pat. No. 4,733,665 (Palmaz), U.S. Pat. No. 4,739,762 (Palmaz), U.S. Pat. No. 4,800,882 (Gianturco), U.S. Pat. No. 4,907,336 (Gianturco), U.S. Pat. No. 5,035,706 (Gianturco et al.), U.S. Pat. No. 5,037,392 (Hillstead), U.S. Pat. No. 5,041,126 (Gianturco), U.S. Pat. No. 5,102,417 (Palmaz), U.S. Pat. No. 5,147,385 (Beck et al.), U.S. Pat. No. 5,282,824 (Gianturco), U.S. Pat. No. 5,316,023 (Palmaz et al.), Canadian patent 1,239,755 (Wallsten), Canadian patent 1,245,527 (Gianturco et al.), Canadian patent application number 2,134,997 (Penn et al.), Canadian patent application number 2,171,047 (Penn et al.), Canadian patent application number 2,175,722 (Penn et al.), Canadian patent application number 2,185,740 (Penn et al.), Canadian patent application number 2,192,520 (Penn et al.), International patent application PCT/CA97/00151 (Penn et al.), International patent application PCT/CA97/00152 (Penn et al.), and International patent application PCT/CA97/00294 (Penn et al.), for a discussion on previous stent designs and deployment systems.
Furthermore, the administration of stents that carry therapeutic coatings, such as one or more polymeric coatings including pharmacologically active agents, have been utilized to reduce some of the problems created by the implantation of stents, such as restinosis and other biocompatibility responses to the foreign implant. Therefore, the search to find optimum materials and coatings, which enhance biocompatibility and prevent the occlusion of the passage through clotting or tissue growth is the ultimate goal of many manufacturers.